airport designations

FlightAware General
1

Does anyone know why FlightAware puts a “K” in front of airport designations such as KPHL for PHL. Thanks.

2

ICAO code.

K’s and P’s for most U.S. airports ( eg. KORD for Chicago). C’s for most Canadian ( CYUL for Montreal ). E’s for European ( EINN for Shannon )

3

We use ICAO airport (and airline) codes instead of IATA airport (and airline) codes.

4

Thanks